Check for async errors in

lib/pure/asyncdispatch.nim

@@ -923,9 +923,17 @@ else:
     var retFuture = newFuture[void]("connect")
 
     proc cb(fd: TAsyncFD): bool =
-      # We have connected.
-      retFuture.complete()
-      return true
+      var ret = SocketHandle(fd).getSockOptInt(cint(SOL_SOCKET), cint(SO_ERROR))
+      if ret == 0:
+          # We have connected.
+          retFuture.complete()
+          return true
+      elif ret == EINTR:
+          # interrupted, keep waiting
+          return false
+      else:
+          retFuture.fail(newException(OSError, osErrorMsg(OSErrorCode(ret))))
+          return true
 
     var aiList = getAddrInfo(address, port, af)
     var success = false

tests/async/tasyncconnect.nim

@@ -0,0 +1,33 @@
+discard """
+  file: "tasyncconnect.nim"
+  exitcode: 1
+  outputsub: "Error: unhandled exception: Connection refused [Exception]"
+"""
+
+import
+    asyncdispatch,
+    posix
+
+
+const
+    testHost = "127.0.0.1"
+    testPort = Port(17357)
+
+
+when defined(windows) or defined(nimdoc):
+    discard
+else:
+    proc testAsyncConnect() {.async.} =
+        var s = newAsyncRawSocket()
+
+        await s.connect(testHost, testPort)
+
+        var peerAddr: SockAddr
+        var addrSize = Socklen(sizeof(peerAddr))
+        var ret = SocketHandle(s).getpeername(addr(peerAddr), addr(addrSize))
+
+        if ret < 0:
+            echo("`connect(...)` failed but no exception was raised.")
+            quit(2)
+
+    waitFor(testAsyncConnect())